260E - How do you tell if a catalytic converter is bad?

My 260E is pumping out black smoke. I've had it to a Mercedes dealer with no luck and talked to another Mercedes mechanic who is stumped. The cat gets hot but not red. When I first start it up, black soot comes out of the tail pipe. I have replaced the O2 sensor, the temperature sensor, the overvoltage relay, and am thinking about replacing the electrohydraulic actuator.

Also the car runs ok when it's cold but as it warms up, the economy needle drops and smoke starts coming out the exhaust.

Any help will be appreciated.

[Benzmac]

This sounds like a fuel control problem. When the cat blocks up, it will usually stall down the engine. I've seen sometimes when the O2 wire will hit ground and cause this.

------------------
Benzmac:
Donnie Drummonds
1991 GMC Syclone
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

[420SEL]

How does the exhaust smell? I have heard that if you are smelling a really bad rotten egg or sulpher smell it is the cat.



------------------
Jason Priest
1986 420SEL

Thanks, I will check for the O2 grounding to see what that looks like. When I put a new O2 in, the car ran much better for a couple of days and then got worse rapidly. The exhaust smells extremely strong and different but it is not quite that rotten egg smell I've smelled from other CATs. Thanks for the help.

sounds really rich. if the coldstart valve hangs ,that could do it, but I don't understand the clearing up w/ a new o2 sensor.I wouldn't think that there would be enough control range to compensate for a stuck coldstart without the engine runing really bad at idle.Has anyone turned the mix adjustment clockwise?The fuel distributor may be dumping at the plunger, into the air sensor housing . U could look in there w/ a flashlight after the engine runs a few seconds and see if it's wet. Becarful to take the cig out of your mouth while you're looking (G)